Attempt to get an offscreen (pbuffer) render wrapper working

This does *not* work correctly unless you have an actual display,
so it's somewhat useless/broken. What we want is a way to get a
pbuffer context without needing a display, and EGL_DEFAULT_DISPLAY
doesn't seem like the correct value.

tests/egltest.py

@@ -1,15 +1,15 @@
 """EGL Pygame test framework"""
 from __future__ import print_function
+import os
+if not os.environ.get( 'PYOPENGL_PLATFORM' ):
+    os.environ['PYOPENGL_PLATFORM'] = 'egl'
 import ctypes
 import pygame.display 
 import pygame 
-import os 
 import logging
 import OpenGL
 from functools import wraps
 
-if not os.environ.get( 'PYOPENGL_PLATFORM' ):
-    os.environ['PYOPENGL_PLATFORM'] = 'egl'
 if os.environ.get( 'TEST_NO_ACCELERATE' ):
     OpenGL.USE_ACCELERATE = False
 

tests/os_egl.py

@@ -0,0 +1,100 @@
+from __future__ import print_function
+import os
+if not os.environ.get( 'PYOPENGL_PLATFORM' ):
+    os.environ['PYOPENGL_PLATFORM'] = 'egl'
+import logging, contextlib
+from functools import wraps
+from OpenGL.GL import *
+from OpenGL.EGL import *
+from OpenGL import arrays
+log = logging.getLogger( __name__ )
+
+API_MAP = {
+    EGL_OPENGL_BIT:EGL_OPENGL_API,
+    EGL_OPENGL_ES2_BIT:EGL_OPENGL_ES_API,
+    EGL_OPENGL_ES_BIT:EGL_OPENGL_ES_API,
+}
+
+def write_ppm(buf, filename):
+    f = open(filename, "w")
+    if f:
+        h, w, c = buf.shape
+        print( "P3", file=f)
+        print( "# ascii ppm file created by os_egl",file=f)
+        print( "%i %i" % (w, h),file=f)
+        print("255",file=f)
+        for y in range(h - 1, -1, -1):
+            for x in range(w):
+                pixel = buf[y, x]
+                l = " %3d %3d %3d" % (pixel[0], pixel[1], pixel[2])
+                f.write(l)
+            f.write("\n")
+
+
+@contextlib.contextmanager
+def egl_context(
+    width=400,
+    height=400, 
+    api=EGL_OPENGL_BIT,
+    attributes = (
+        EGL_BLUE_SIZE, 8,
+        EGL_RED_SIZE,8,
+        EGL_GREEN_SIZE,8,
+        EGL_DEPTH_SIZE,24,
+        EGL_COLOR_BUFFER_TYPE, EGL_RGB_BUFFER,
+        EGL_CONFIG_CAVEAT, EGL_NONE, # Don't allow slow/non-conformant
+        EGL_SURFACE_TYPE, EGL_PBUFFER_BIT,
+    ),
+    output='output.ppm',
+):
+    """Setup a context for rendering"""
+    major,minor = GLint(), GLint()
+    display = eglGetDisplay(EGL_DEFAULT_DISPLAY)
+    if display == EGL_NO_DISPLAY:
+        raise RuntimeError(EGL_NO_DISPLAY, )
+    # print("Display: %s"%(display.address,))
+    eglInitialize( display, major, minor)
+    num_configs = GLint()
+    configs = (EGLConfig*2)()
+    local_attributes = list(attributes[:])
+    local_attributes.extend( [
+        # EGL_CONFORMANT, api,
+        EGL_NONE, # end of list
+    ])
+    log.info("Attributes: %s", local_attributes)
+    local_attributes= arrays.GLintArray.asArray( local_attributes )
+    try:
+        eglChooseConfig(display, local_attributes, configs, 2, num_configs)
+        surface_attributes = [
+            EGL_WIDTH,width,
+            EGL_HEIGHT,height,
+            EGL_NONE,
+        ]
+        surface = eglCreatePbufferSurface(
+            display, 
+            configs[0],
+            surface_attributes,
+        )
+    except GLError as err:
+        log.error("Error code: %s on %s", err.err, err.baseOperation)
+        raise
+    eglBindAPI(API_MAP[api])
+    ctx = eglCreateContext(display, configs[0], EGL_NO_CONTEXT, None)
+    if ctx == EGL_NO_CONTEXT:
+        raise RuntimeError( 'Unable to create context' )
+    eglMakeCurrent( display, surface, surface, ctx )
+    yield ctx,surface 
+    content = glReadPixelsub(0,0, width, height, GL_RGB, outputType=None)
+    if output:
+        write_ppm(content, output)
+    # eglSwapBuffers( display, surface )
+
+def main():
+    with egl_context() as setup:
+        ctx,surface = setup
+        glClearColor(1.0,1.0,1.0,1.0)
+        glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT)
+
+if __name__ == '__main__':
+    logging.basicConfig(level=logging.INFO)
+    main()